Control method and apparatus for a single shaft turbine with prewhirl of air entering the compressor

ABSTRACT

A vehicle turbine propels the vehicle through a change-speed transmission. To reduce vehicle acceleration time with an acceptable penalty with respect to fuel consumption, the compressor of the engine has variable inlet guide vanes which are shifted into a positive prewhirl angle at idling speeds when the transmission is shifted into a drive condition. Thus the engine has a low speed idle, with axially oriented guide vanes and normal air entrance, when the transmission is in neutral or park, and a high speed idle with positive prewhirl when the transmission is in a drive condition. Also, the vanes are shifted at full speed of the engine to provide negative prewhirl and thus reduce the engine speed corresponding to maximum power output. Because of the higher idle and lower maximum speeds, the acceleration time of the turbine is reduced.

United States Patent [191 Amann et al.

[ 1*Mar. 19, 1974 CONTROL METHOD AND APPARATUS FOR A SINGLE SHAFT TURBINE WITH PREWHIRL OF AIR ENTERING THE COMPRESSOR Inventors: Charles A. Amann, Bloomfield Hills;

Erik H. Rucins, Sterling Heights, both of Mich.

General Motors Corporation, Detroit, Mich.

The portion of the term of this patent subsequent to Apr. 25, 1989, has been disclaimed.

Filed: Aug. 9, 1972 Appl. No.: 279,200

Related US. Application Data Continuation-impart of Ser. No. 194,116, Nov. 1, 1971, Pat. No. 3,688,605, which is a division of Ser. No. 854,651, Sept. 2, 1969, Pat. No. 3,657,881.

Assignee:

Notice:

US. Cl. 60/3903, 60/3929, 74/DlG. 5 Int. Cl. F02c 9/14 Field of Search 60/3903, 39.29, 39.04,

60/3916 R; 74/860, 864, DIG. 5

References Cited UNITED STATES PATENTS 3,688,605 Amann 60/39.l6 R

TRANSDUCER 3,657,881 4/1972 Amann 60/3916 R Primary ExaminerClarence R. Gordon Attorney, Agent, or Firm-Paul Fitzpatrick [57] ABSTRACT A vehicle turbine propels the vehicle through a change-speed transmission. To reduce vehicle acceleration time with an acceptable penalty with respect to fuel consumption, the compressor of the engine has variable inlet guide vanes which are shifted into a positive prewhirl angle at idling speeds when the transmission is shifted into a drive condition. Thus the engine has a low speed idle, with axially oriented guide vanes 4 Claims, 3 Drawing Figures (I TRANSMISSION it: LOAD RESERVOIR PATENIEnm 19 m4 TRANSMISSIONII. LOAD I l U2 SPEED TRANSDUCER 1 A III f RESERVOIR OZClrmm PER CENT GASIFIER RPM CONTROL METHOD AND APPARATUS FOR A SINGLE SHAFT TURBINE WITH PREWHIRL OF AIR ENTERING THE COMPRESSOR This application is a continuation-in-part of our application Ser. No. 194,] 16 for Turbine Control Method filed Nov. 1, 1971 now U.S. Pat. No. 3,688,605, which is a division of our application Ser. No. 854,651 for Turbine Control filed Sept. 2, 1969 now U.S. Pat. No. 3,657,881.

This invention relates to gas turbine power plants, to

make them better suited to the requirements for power plants for automotive vehicles. It is particularly directed to a method of improving the acceleration characteristics from idle to medium or full load of a single shaft turbine powering a vehicle.

' Along with their many advantages, gas turbines have significant disadvantages for vehicle propulsion as compared, for example, to gasoline reciprocating engines and diesel engines.

One of these disadvantages is relatively high fuel consumption at idle, particularly with relation to that of the diesel engine. Another disadvantage is a substantial time lag between idle and full power which is undesirable in stop and go driving. It is, thus, highly desirable to find means to improve the acceleration and the part load fuel consumption characteristics of such engines.

The acceleration characteristics of the usual gas turbine engine can be greatly improved by increasing the idle speed of the engine. In the ordinary gas-coupled engine, the minimum satisfactory gas generator idle speed is somewhere near 50 percent of the speed at full power. By stepping up the idle speed to, say, 75 percent, the time required for the gas generator to accelerate to full power output is greatly reduced. As a matter of fact, it is possible to idle the engine at 100 percent gas generator speed by braking the power turbine. However, such high speed idling greatly increases the fuel consumption while the vehicle is stationary.

It is also desirable, for convenience in driving the vehicle, to have the torque of the power turbine sufficiently low when the gas generator is idling that it is not necessary to hold the vehicle brakes engaged to prevent vehicle creep. It is desirable to have a characteristic similar to that of a gasoline engine with a torque converter which idles at a speed sufficiently low that the torque converter transmits too small a torque to move the vehicle.

When the gas generator turbine provides the shaft power output, as in the usual single-shaft gas turbine, the idle speed remains high and acceleration time remains a problem. Also it remains desirable to minimize idle fuel comsumption.

The principle of this invention is based upon the conclusion that the idle speed of the gas generator turbine may be substantially increased, by imparting substantial positive prewhirl to the air entering the compressor. Positive prewhirl is a tangential component of air velocity in the direction of rotation of the compressor. Also, to minimize waste of fuel when the vehicle is not in the ready condition for operating, this prewhirl is eliminated when the transmission is put into neutral or park conditions and the engine is then allowed to idle at a low speed idle. Also, the speed of the gas generator at maximum horsepower output is reduced somewhat by imparting negative prewhirl (that is, whirl opposite to compressor rotation) to the air entering the compressor when operating near maximum gas generator speed. By these means, a reduction of approximately one-third in the difference between ready idle and full power gas generator speeds may be achieved, with a corresponding very substantial reduction in acceleration time, particularly since the acceleration of the gas generator through the lower part of its speed range is slower than through the higher part of its speed range.

When the engine is of a single-shaft type, with the gas generator turbine driving the power output shaft directly, the same principle of varying inlet air swirl to reduce acceleration time and reduce idle fuel consumption applies. However, since engine output shaft speed is fairly high at idle, the transmission must effectively disengage when the vehicle is at a standstill.

The prewhirl may be controlled by variable-setting inlet guide vanes in the engine compressor.

The nature of the invention and its advantages will be clear to those skilled in the art from the succeeding detailed description of the preferred embodiment of the invention and the accompanying drawings.

FIG. 1 is a schematic diagram of a vehicle gas turbine installation including controls according to the invention.

FIG. 2 is a frontal view of the engine compressor inlet.

FIG. 3 is a graphical representation of operating conditions at different speeds and vane angle conditions.

FIG. 1 illustrates schematically a single-shaft gas turbine engine which, as is customary, includes a dynamic compressor 7, a combustion apparatus 8, and a gas generator turbine 10. Turbine 10 includes a rotor which drives compressor 7 through a shaft 11, and compressed air flows from the compressor 7 to the combustion apparatus 8 to which fuel is also supplied through a fuel line 12. The fuel is burned in the compressed air and the resulting combustion products flow to turbine 10 to energize it.

As illustrated, the engine is non-regenerative although, of course, a regenerator may be included without affecting this invention. The turbine 10 also drives through a power output shaft 15 into a transmission or change gear box 16 of any suitable type. The transmission drives a load 18 which, in the preferred environment of the invention, is the driving wheels of a motor vehicle.

A single-shaft engine for driving a vehicle requires a transmission that will allow the turbine to continue to operate at least at idle speed, and preferably at full speed when desired, with the vehicle at a standstill. While an ordinary mechanical or automatic transmission including some sort of clutch may be used, there are reasons to prefer an infinitely variable transmission (mechanical, hydraulic, or electrical) which may include declutching means or other means to provide a tending radially of the guide vane ring and being movable by an arm 23. The arms 23 are all pivotally connected to an actuating ring 24 encircling the compressor. Ring 24 may be rotated by actuating means to be described to vary the setting or angle of the inlet guide vanes.

The inlet structure is shown more structurally in FIG. 2 which also illustrates a center bullet or fairing 26 of the inlet, and a number of variable setting vanes 22. The compressor 7 may be axial-flow or may be centrifugal as in the patents referred to above.

In the described embodiment of the invention, the ring 24 is actuated by a three-position hydraulic actuator 27 which comprises two double-acting hydraulic cylinders fixed together in tandem with one piston rod extending from each end of the actuator. Thus, one cylinder 28 has reciprocable therein a piston and rod assembly 30 and the other cylinder 31 has therein a piston and piston rod assembly 32, the piston rod 32 being connected to a fixed structure at 34. Piston rod 30 is suitably connected by means such as a pin 35 to the actuating ring 24. As applied here, the actuator 27 can move the ring 24 to three positions; one when both pistons are at the inner ends of the cylinders, one when piston 30 is at the outer end, and one when both pistons are at the outer ends of the cylinders. The particular structure of the actuator 27 is not material to this invention, since any suitable three position actuating device may be used or, if desired, a multi-position actuator device. One suitable type of actuator is described in detail fn Sfiort et alUTSTpa'tent No. 2,893,353 to? Three Position Actuator Cylinder.

The transmission 16 is a suitable form of change speed gear to adapt the torque characteristics of the engine to the requirements of the load. The details of the transmission are immaterial to this invention but it preferably is a power-shift transmission and one in which the transmission controls include a neutral position and at least one drive position. One example of such a transmission is that disclosed in Spreitzer et al. US. Pat. No. 3,093,0l0. A transmission of this type may be used, but an infinitely variable transmission has advantages and might be preferred. As illustrated schematically in the drawing, transmission 16 includes a control lever 37 which may be manually operated and which has a neutral position indicated by N and at least one drive position indicated by D. This is a power disconnect, and in some cases might be some sort of clutch integral with or separate from the transmission. The transmission includes a normally open switch 36 which is closed whenever the control is moved to the drive position. Alternatively, switch 36 could be a normally closed switch which is held open only when the control lever is in neutral position.

Switch 36 controls the supply of actuating fluid to the actuator 27 in connection with means responsive to the speed of the trubine indicated as a speed transducer 38 driven from the shaft 1 1 through gearing and accessory drive shaft 39. This can be any suitable device effective to move an output element as a function of speed of turbine 10. The transducer 38 controls a normally closed switch A and a normally open switch B.

Switches A and B control two solenoid-actuated reversing valves 40 and 42 which control the supply of actuating fluid to the cylinders 28 and 31 of actuator 27. In the illustrated embodiment, the fluid is hydraulic fluid supplied from a reservoir 43 under pressure by a pump 44 which may, for example, be driven from the gas generator shaft 11, and may also, if desired, be the lubricating pump of the engine.

As illustrated, the pump 44 supplies fluid through a branch line 46 to valve 40 and through a branch line 47 to valve 42. These valves are connected back to the reservoir by return lines 48 and 50, respectively. These valves 40 and 42 simply serve to connect the actuating cylinders either normally or reversely to the pump to cause the piston to be driven to one end or the other of the cylinder 28 or 31 in which it reciprocates.

The fluid pressure system could, if desired, be an air pressure system, and specifically the actuator of the Short et al patent referred to above is adapted for actuation by compressed air.

The speed transducer 38 moves a switch operating plunger 51 which bears lugs which actuate the switches A and B. In the particular embodiment here described, normally closed switch A is opened by the plunger 51 at approximately 58 percent full speed of turbine 10 and remains open at higher speeds, and switch B remains open until turbine 10 reaches approximately percent full speed, at which point it is closed and remains closed at higher speeds. A suitable energizing circuit for the solenoid valves is indicated by a circuit from ground through a battery 54 and a positive line 55 to switch B by which it is connected to energizing line 56 for solenoid valve 42, which is connected to ground. When the solenoid valve 42 is not energized, the pressure line 47 is connected through a line 58 to hold the piston and rod assembly 30 in the short cylinder 28 extended and the outer end of the cylinder is connected through line 59 and valve 42 to the return line 50. The inlet vanes 22 are then set at 0 prewhirl. When the solenoid is energized, the connections to lines 58 and 59 are reversed and the piston 30 is pulled inward to shift the ring 24 and move the vanes to the minus 20 setting. Thus, the vanes are moved to this minus 20 setting at top speed of turbine 10, above about 95 percent rated.

Solenoid valve 40 is likewise shown in its deenergized condition, in which fluid is conducted from pump output line 46 through a line 60 to the outer end of cylinder 31 to hold the piston and rod assembly 32 retracted into the cylinder and the inner end of the cylinder 31 is connected through a line 62 and valve 40 to the return line 48. The valve is shown deenergized because, although switch A is shown closed, switch 36 is open. Now, if the transmission control 35 is shifted into a drive position, switch 36 is closed to complete a circuit from line 55 through switch 36, line 63, switch A, which is assumed closed, to the solenoid valve 40 to reverse the connection to cylinder 31 to extend the piston and rod 32 and move the vanes 22 to the plus 60 prewhirl position.

As previously stated, switch A is closed below approximately 58 percent speed and opens at 5 8 percent speed to reverse the connection to cylinder 31 of actuator 27 and thus restore the vanes to the zero prewhirl position. This sequence of events is indicated by the line M on the chart of FIG. 3 which, as will be seen, indicates the vanes as being at plus 60 below 58 percent speed, shifting to 0 at 58 percent, remaining at 0 to 95 percent, then shifting to minus 20 from 95 to percent speed of turbine 10. The broken line N indicates the override by the switch 36 which, when it is open, causes the vanes to return to the 0 position for normal low speed or standby idle operation of the power plant.

As previously stated, the purpose of the positive prewhirl is to allow faster idle operation of the gas generator. The gas generator will not automatically speed up because of the change of inlet vane angle if it is controlled, as is usually the case, by a governor. Gas turbines ordinarily have a fuel control which provides for control of power output and assures safe operation of the engine without surge, overspeed, overheating, flameout, and other disturbances of the operation. One element of the fuel control system of the usual gas turbine engine is an adjustable governor which controls the speed of operation of the gas generator.

In the preferred embodiment illustrated herein, the control to implement the invention is effected by a gas generator governor in the fuel control. Referring to FIG. 1, a fuel control 64 is supplied with fuel under pressure from any suitable source through a line 67 and meters fuel to the engine through the line 12 extending to the combustion apparatus 8. The control 64 receives an input of gas generator speed from shaft 39 and suitable transmission means illustrated by the gearing and shaft 70. Additionally, the control 64 receives an input of desired power output or gas generator speed which is transmitted from a control indicated as a foot throttle pedal 72 through linkage 74 to a swinging input arm 75 on the fuel control. Arm 75 may be considered to be biased counterclockwise or in the direction of decreasing speed and power by a tension spring 76. The minimum speed position of arm 75 is determined by a movable stop 78 which has a position of rest in which the arm 75 moves to the minimum power or standby idle position and a second position in which the arm 75 is held farther in the counterclockwise direction to call for a higher idle speed. The variable stop 78 is moved to the high speed position by suitable means such as solenoid 79 energized from line 63 whenever the transmission switch 36 is closed.

Thus, the engine may operate at a low speed idle with the inlet vanes at and the transmission in neutral. When the transmission is shifted to a drive condition, the vanes are shifted to 60 positive prewhirl as shown on the line M in FIG. 3. At the same time, the stop 78 is energized to boost the speed setting of the gas generator governor to cause it to run just below the 58 percent speed point.

As the foot throttle 72 is actuated to cause the vehicle to move off, the governor setting is raised and the gas generator speeds up, causing the speed transducer 38 to open switch A and thereby put the inlet guide vanes back to the zero prewhirl position. Finally, as the power is increased and the engine accelerates toward maximum gas generator speed, the switch B is closed and the vanes are given a minus 20 setting for full power operation.

The effect of this may be appreciated more clearly from the curves indicated as X, Y, and Z in FIG. 3. Curve X represents the operation of a gas-coupled engine with minus 20 prewhirl through the speed range from idle below 50 percent speed to 100 percent speed at full power. Note that gas horsepower supplied to the power turbine increases from about 8 percent to about 100 percent over this speed range. The curve Y indicates operation with the vanes set at 0, in which case the power output is lower and finally increases to about 8 percent normal at full speed. The curve Z indicates the result of operation with the positive prewhirl with the result that the power output is very much less than the value associated with normal operation of the engine. Thus, the higher idle speed may be maintained without generation of sufficient gas horsepower to create objectionable creep problems in the vehicle, since gas horsepower and therefore power turbine torque remain low.

If the engine is single-shaft, the higher speed idle re mains desirable to minimize the time lag between idle and full (or higher) power output of the engine. Also, the reduction of idle fuel consumption by the positive prewhirl increases economy and tends to reduce exhaust emissions.

The detailed description of the preferred embodiment of the invention for the purpose of explaining the principles thereof is not to be regarded as limiting the invention, as various modifications may be made by the exercise of skill in the art.

We claim:

1. A method of operating a single-shaft gas turbine engine including a dynamic compressor having means for varying compressor inlet prewhirl, combustion apparatus supplied by the compressor, a turbine supplied with motive fluid by the combustion apparatus, the turbine having a rotor connected to drive the compressor, and including a power transmission having neutral and power-transmitting conditions connecting the turbine rotor to a load, so as to reduce idling fuel consumption of the engine and reduce acceleration time of the engine from idling to full power operating condition, comprising operating the engine with minimal compressor inlet prewhirl at a low idle speed when the transmission is in a neutral condition, operating the engine at a ready idle speed higher than the low idle speed when the transmission is in a power-transmitting condition with substantial positive compressor inlet prewhirl to provide minimal power output from the engine, operating the engine with minimal positive compressor inlet prewhirl over a range of speed from ready idle to near full rated speed to provide a range of power output from the engine, and operating the engine with substantial negative compressor inlet prewhirl during operation at substantially full rated speed.

2. A single-shaft gas turbine vehicle propulsion power plant comprising, in combination, a gas turbine engine including a dynamic compressor having variable inlet means for imparting variable prewhirl to air entering the compressor, combustion apparatus supplied by the compressor, and a turbine supplied by the combustion apparatus including a rotor coupled to drive the compressor; power transmission means coupling the said turbine rotor to a load, the power transmission means including means for setting it into a neutral condition and into at least one drive condition; means responsive to the transmission setting means and to turbine rotor speed effective to set the inlet means to impart substantial positive prewhirl when the transmission setting is other than neutral and gas generator speed is below a high idle limit; and means responsive to gas generator speed effective to set the inlet means to impart substantial negative prewhirl when gas generator speed is near maximum rated speed.

3. A single-shaft gas turbine vehicle propulsion power plant comprising, in combination, a gas turbine engine including a dynamic compressor having variable setting inlet guide vanes for imparting prewhirl to air entering the compressor, combustion apparatus supplied by the compressor, and a turbine supplied by the combustion apparatus including a rotor coupled to drive the compressor; power transmission means coupling the said turbine rotor to a load, the power transmission means including means for setting it into a neutral condition and into at least one drive condition; means responsive to the transmission setting means and to turbine rotor speed effective to set the inlet guide vanes to a position to impart substantial positive prewhirl when the transmission setting is other than neutral and gas generator speed is below a high idle limit; and means responsive to turbine rotor speed effective to adjust the inlet guide vanes to a position to impart substantial negative prewhirl when the speed is near maximum rated.

4. A single-shaft gas turbine vehicle propulsion power plant comprising, in combination, a gas turbine engine including a dynamic compressor having variable setting inlet guide vanes for imparting prewhirl to air entering the compressor, combustion apparatus supplied by the compressor, and a turbine supplied by the combustion apparatus including a rotor coupled to drive the compressor; power transmission means coupling the said turbine rotor to a load, the power transmission means including means for setting it into a neutral condition and into at least one drive condition; means responsive to the transmission setting means and to turbine rotor speed effective to set the inlet guide vanes to a position to impart substantial positive prewhirl when the transmission setting is other than neutral and gas generator speed is below a high idle limit; means responsive to turbine rotor speed effective to adjust the inlet guide vanes to a position to impart substantial negative prewhirl when the speed is near maximum rated; and means effective otherwise to set the inlet guide vanes to a position to impart minimal prewhirl. 

1. A method of operating a single-shaft gas turbine engine including a dynamic compressor having means for varying compressor inlet prewhirl, combustion apparatus supplied by the compressor, a turbine supplied with motive fluid by the combustion apparatus, the turbine having a rotor connected to drive the compressor, and including a power transmission having neutral and power-transmitting conditions connecting the turbine rotor to a load, so as to reduce idling fuel consumption of the engine and reduce acceleration time of the engine from idling to full power operating condition, comprising operating the engine with minimal compressor inlet prewhirl at a low idle speed when the transmission is in a neutral condition, operating the engine at a ready idle speed higher than the low idle speed when the transmission is in a power-transmitting condition with substantial positive compressor inlet prewhirl to provide minimal power output from the engine, operating the engine with minimal positive compressor inlet prewhirl over a range of speed from ready idle to near full rated speed to provide a range of power output from the engine, and operating the engine with substantial negative compressor inlet prewhirl during operation at substantially full rated speed.
 2. A single-shaft gas turbine vehicle propulsion power plant comprising, in combination, a gas turbine engine including a dynamic compressor having variable inlet means for imparting variable prewhirl to air entering the compressor, combustion apparatus supplied by the compressor, and a turbine supplied by the combustion apparatus including a rotor coupled to drive the compressor; power transmission means coupling the said turbine rotor to a load, the power transmission means including means for setting it into a neutral condition and into at least one drive condition; means responsive to the transmission setting means and to turbine rotor speed effective to set the inlet means to impart substantial positive prewhirl when the transmission setting is other than neutral and gas generator speed is below a high idle limit; and means responsive to gas generator speed effective to set the inlet means to impart substantial negative prewhirl when gas generator speed is near maximum rated speed.
 3. A single-shaft gas turbine vehicle propulsion power plant comprising, in combination, a gas turbine engine including a dynamic compressor having variable setting inlet guide vanes for imparting prewhirl to air entering the compressor, combustion apparatus supplied by the compressor, and a turbine supplied by the combustion apparatus including a rotor coupled to drive the compressor; power transmission means coupling the said turbine rotor to a load, the power transmission means including means for setting it into a neutral condition and into at least one drive condition; means responsive to the transmission setting means and to turbine rotor speed effective to set the inlet guide vanes to a position to impart substantial positive prewhirl when the transmission setting is other than neutral and gas generator speed is below a high idle limit; and means responsive to turbine rotor speed effective to adjust the inlet guide vanes to a position to impart substantial negative prewhirl when the speed is near maximum rated.
 4. A single-shaft gas turbine vehicle propulsion power plant comprising, in combination, a gas turbine engine including a dynamic compressor having variable setting inlet guide vanes for imparting prewhirl to air entering the compressor, combustion apparatus supplied by the compressor, and a turbine supplied by the combustion apparatus including a rotor coupled to drive the compressor; power transmission means coupling the said turbine rotor to a load, the power transmission means including means for setting it into a neutral condition and into at least one drive condition; means responsive to the transmission setting means and to turbine rotor speed effEctive to set the inlet guide vanes to a position to impart substantial positive prewhirl when the transmission setting is other than neutral and gas generator speed is below a high idle limit; means responsive to turbine rotor speed effective to adjust the inlet guide vanes to a position to impart substantial negative prewhirl when the speed is near maximum rated; and means effective otherwise to set the inlet guide vanes to a position to impart minimal prewhirl. 